Patent Document 1 discloses a turbocharger of twin-scroll type to be applied to a multi-cylinder and high-displacement engine for a ship or the like. Such a turbocharger has a turbine casing including a shroud that defines an operational flow path between a hub of a turbine rotor and the shroud, a scroll outer peripheral wall continuing from one end side of the shroud and extending along the circumferential direction of the shroud, and a partition wall disposed inside the scroll outer peripheral wall and dividing the inside space of the scroll outer peripheral wall into the first scroll flow path and the second scroll flow path disposed adjacent to each other in the axial direction of the shroud.
The scroll outer peripheral wall has a tongue section at the most downstream position thereof. The partition wall extends up to the position of 200 degrees in the circumferential direction of the shroud, where the position in the circumferential direction of the shroud is represented with reference to the position of the tongue section as the zero-degree position, and the flowing direction of the fluid as the positive direction. Further, a coating layer is formed on an inner wall of a downstream region (a region from 200 to 360 degrees in the circumferential direction of the shroud) where the partition wall is not provided. According to the document, the above configuration effectively suppresses occurrence of erosion due to collision of particles in a fluid (exhaust gas) in the downstream region without the partition wall.
Patent Document 2 discloses a turbine casing including three cast components: a turbine-side component, an intermediate component, and an exhaust-side component. The turbine-side component, the intermediate component, and the exhaust-side component are welded at butting surfaces and integrated into one piece. The turbine-side component forms the shroud and a part of the scroll outer peripheral wall, while the intermediate component forms another part of the scroll outer peripheral wall and the partition wall. The exhaust-side component forms the remaining part of the scroll outer peripheral wall. According to the document, such a turbine casing has a small thickness and a small weight, as well as a smooth-surfaced flow path that carries a fluid (exhaust gas).